This invention relates generally to fire detectors, and more particularly to flame detecting apparatus having ultraviolet (UV) flame detecting means to trigger an audible alarm upon the detection of UV radiation from a fire. The flame detecting apparatus is provided with protection means to protect the UV detecting means while simultaneously maintaining sufficient exposure of the UV detecting means for detecting the presence of UV radiation.
It is known that fires produce a detectable amount of UV radiation. The concept of providing UV-sensitive detectors for fire detection systems has been shown in the prior art. However, a problem existing in this area is that the UV detector, usually a photodiode, is quite fragile and needs to be protected from possible damage that could occur from installation, removal, and/or repair of the fire detector. Furthermore, in areas where ceilings may be low or in areas where objects are substantially close to the fire detector, it is desirable to provide effective protection of the UV detector. This protection, however, must not significantly reduce the sensitivity of the UV detector. Namely, the UV detector must not be covered or surrounded by any material which would interfere with its ability to detect the presence of UV radiation, while at the same time, the UV detector must be adequately protected from possible damage.
In addition, primarily in order to protect these prior devices, it has been necessary to mount these devices in the nature of a camera, at a location "aimed" at a specified area, and thus not achieving 360.degree., or non-directional exposure. The prior art has not adequately addressed these problems of providing the necessary protection of a UV detector while sufficiently exposing the detector to detect UV radiation emitted from a fire.
In Trumble, U.S. Pat. No. 3,775,762, a fire detecting system is disclosed that is intended to reliably discriminate between UV radiation from a flame and UV radiation from other emitting sources. However, this system is primarily directed at a logic circuit for accomplishing such discrimination, and fails to disclose any type of protection means for the detector or even a structural housing for protecting the UV detector while maintaining sufficient exposure to the surrounding area.
Wendt, U.S. Pat. No. 4,455,487, and Spector et al., U.S. Pat. No. 4,765,413, disclose radiation detection apparatus that utilizes both UV and IR (infrared) radiation detection to increase reliability in discriminating between flame and non-flame radiation. Similarly, both references lack a housing structure with protection means to protect and sufficiently expose either the UV or IR detectors.
In Hemme, U.S. Pat. No. 3,990,518, an automatic fire alarm and extinguishing device with a housing is disclosed. Fire sensing elements are disposed to project through openings in the housing, and although the detectors are exposed to the surrounding area, they are unprotected from possible damage.
Seki et al., U.S. Pat. No. 4,639,605, discloses a fire sensor device having a condenser lens disposed in front of a photoelectric conversion element. However, UV radiation must pass through the lens before reaching the detector and thus the detector must be situated behind the lens and thus cannot be sufficiently exposed to the surrounding area.
In Cholin, U.S. Pat. No. 4,241,258, a UV translating detection device is disclosed which utilizes phosphor to translate UV wavelengths into visible or near-IR wavelengths. This translation process, however, involves the use of either quartz and glass windows together, a quartz prism, or a diffraction grating through which the UV radiation must pass. After passing through a window or prism, the UV radiation is directed to a layer of phosphor which will then fluoresce when exposed to the UV radiation. This florescence of the phosphor is then detected by photosensitive solid state detection cells.
The UV translation process described in Cholin has some deficiencies. Namely, the translation system can be costly by requiring the use of quartz and glass windows together, prisms, or diffraction gratings, through which the UV radiation must pass. Additionally, the use of a window composed of quartz or glass may fail to provide adequate fire detection, namely because some amount of UV radiation will not transmit through these materials. Furthermore, the UV detector is enclosed completely within the housing and as such, will not be optimally exposed to the surrounding area for the maximum detection of UV radiation emitted from a fire.
Accordingly, the present invention attempts to overcome these deficiencies in the prior art by providing flame detecting apparatus having flame detecting means including UV detecting means for triggering an audible alarm upon the detection of a predetermined amount of UV radiation. Furthermore, protective means are provided to protect the UV detecting means and to sufficiently expose the UV detecting means to the surrounding area to detect UV radiation emitted from a fire, and to provide 360.degree. coverage to do so in a manner so as to cover as large an area as possible.
Therefore, it is an object of the present invention to provide flame detecting apparatus having UV detecting means protected by protective means while being sufficiently exposed to the surrounding area to detect the presence of UV radiation.
It is another object of the present invention to provide flame detecting apparatus where the protective means includes a plurality of wing members disposed substantially perpendicular to the UV detecting means whereby the wing members do not significantly interfere with the detecting of UV radiation.
It is another object of the present invention to provide flame detecting apparatus where the protective means includes a hollow ring member extending circumferentially around the UV detecting means and attached to the wing members whereby the UV detecting means is protected while remaining sufficiently exposed through the hollow ring member to detect UV radiation.
It is yet another object of the present invention to provide flame detecting apparatus where the protective means is formed as an integral part of the exterior of the housing.
These and other objects will become apparent, as will a better understanding of the concepts underlying the present invention, by reference to the description which follows when taken in conjunction with the accompanying drawings.